1. Field of the Invention
The present invention relates to a fuel cell system, and more particularly, to a reformer for a fuel cell system.
2. Description of the Related Art
A fuel cell system is an electricity generating system that directly converts chemical reaction energy of separately supplied oxygen and hydrogen contained in a hydrocarbon material (e.g., methanol, ethanol, natural gas, etc.) into electrical energy.
A polymer electrolyte membrane fuel cell (PEMFC) is a type of fuel cell that has an excellent output characteristic, a low operating temperature, and fast starting and response characteristics.
In addition, the PEMFC has a wide range of applications including as mobile power sources for vehicles, distributed power sources for homes or other buildings, and small-size power sources for electronic apparatuses.
A fuel cell system employing the PEMFC includes a stack, a reformer, a fuel tank, and a fuel pump.
The stack constitutes a body of the fuel cell for generating electric energy through a reaction of hydrogen and oxygen, and the fuel pump supplies the fuel of the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen (or hydrogen-rich gas) and supplies the hydrogen to the stack.
The reformer generates the hydrogen from the fuel through a chemical catalytic reaction using thermal energy. That is, the reformer includes a heat source unit for generating the thermal energy and a reforming reaction unit for generating the hydrogen from the fuel through a reforming reaction using the thermal energy.
The heat source unit generates the thermal energy through an oxidation reaction of the fuel and oxygen using an oxidation catalyst.
In a conventional reformer, the heat source unit and the reforming reaction unit are separately distributed, and heat generated by the heat source unit is transferred to the reforming reaction unit. Therefore, heat is not directly exchanged between the heat source unit and the reforming reaction unit, so that the conventional reformer has a low heat transfer efficiency.
In addition, since the heat source unit and the reforming reaction unit are separately distributed, it is difficult to implement a compact fuel cell system.
Further, in the conventional reformer, the fuel and oxygen supplied to the heat source unit are non-uniformly (or locally) distributed over the entire oxidation catalyst of the heat source unit, so that the oxidation reaction occurs non-uniformly. Therefore, in the heat source unit, a temperature gradient occurs. The temperature gradient of the heat source unit further deteriorates the performance and thermal efficiency of the reformer.